DESCRIPTION

MongoDBx::Class is a flexible object relational mapper (ORM) for MongoDB databases. Given a schema-like collection of document classes, MongoDBx::Class expands MongoDB objects (hash-refs in Perl) from the database into objects of those document classes, and collapses such objects back to the database.

MongoDBx::Class takes advantage of the fact that Perl's MongoDB driver is Moose-based to extend and tweak the driver's behavior, instead of wrapping it. This means MongoDBx::Class does not define its own syntax, so you simply use it exactly as you would the MongoDB driver directly. That said, MongoDBx::Class adds some sugar that enhances and simplifies the syntax unobtrusively (either use it or don't). Thus, it is relatively easy to convert your current MongoDB applications to MongoDBx::Class. A collection in MongoDBx::Class isa('MongoDB::Collection'), a database in MongoDBx::Class isa('MongoDB::Database'), etc.

As opposed to other ORMs (even non-MongoDB ones), MongoDBx::Class attempts to stay as close as possible to MongoDB's non-schematic nature. While most ORMs enforce using a single collection (or table in the SQL world) for every object class, MongoDBx::Class allows you to store documents of different classes in different collections (and even databases). A collection can hold documents of many different classes. Not only that, as MongoDBx::Class is Moose based, you can easily create very flexible schemas by using concepts such as inheritance and roles. For example, say you have a collection called 'people' with documents representing, well, people, but these people can either be teachers or students. Also, students may assume the role "hall monitor". With MongoDBx::Class, you can create a common base class, say "People", and two more classes that extend it - "Teacher" and "Student" with attributes that are only relevant to each one. You also create a role called "HallMonitor", possibly with some methods of its own. You can save all these "people documents" into a single MongoDB collection, and when fetching documents from that collection, they will be properly expanded to their correct classes (though you will have to apply roles yourself - at least for now).

COMPARISON WITH OTHER MongoDB ORMs

As MongoDB is rather young, there aren't many options out there, though CPAN has some pretty good ones, and will probably have more as MongoDB popularity rises.

The first MongoDB ORM in CPAN was Mongoose, and while it's a very good ORM, MongoDBx::Class was mainly written to overcome some limitations of Mongoose. The biggest of these limitations is that in order to provide a more comfortable syntax than MongoDB's native syntax, Mongoose makes the unfortunate decision of being implemented as a singleton, meaning only one instance of a Mongoose-based schema can be used in an application. That essentially kills multithreaded applications. Say you have a Plack-based (doesn't have to be Plack-based though) web application deployed via Starman (or any other web server for that matter), which is a pre-forking web server - you're pretty much doomed. As MongoDB's driver states, it doesn't support connection pooling, so every fork has to have its own connection to the MongoDB server. Mongoose being a singleton means your threads will not have a connection to the server, and you're screwed. MongoDBx::Class does not suffer this limitation. You can start as many connections as you like. If you're running in a pre-forking environment, you don't have to worry about it at all.

Other differences from Mongoose include:

Mongoose creates its own syntax, MongoDBx::Class doesn't, you use MongoDB's syntax directly.

A document class in Mongoose is connected to a single collection only, and a collection can only have documents of that class. MongoDBx::Class doesn't have that limitation. Do what you like.

Mongoose has limited support for multiple database usage. With MongoDBx::Class, you can use as many databases as you want.

MongoDBx::Class is way faster. While I haven't performed any real benchmarks, an application converted from Mongoose to MongoDBx::Class showed an increase of speed in orders of magnitude.

In Mongoose, your document class attributes are expected to be read-write (i.e. is => 'rw' in Moose), otherwise expansion will fail. This is not the case with MongoDBx::Class, your attributes can safely be read-only.

Another ORM for MongoDB is Mongrel, which doesn't use Moose and is thus lighter (though as MongoDB is already Moose-based, I see no benefit here). It uses Oogly for data validation (while Moose has its own type validation), and seems to define its own syntax as well. Unfortunately, documentation is currently lacking, and I haven't given it a try, so I can't draw specific comparisons here.

Even before Mongoose was born, you could use MongoDB as a backend for KiokuDB, by using KiokuDB::Backend::MongoDB. However, KiokuDB is considered a database of its own and uses some conventions which doesn't fit well with MongoDB. Mongoose::Intro already gives a pretty convincing case when and why you should or shouldn't want to use KiokuDB.

CONNECTION POOLING

Since version 0.9, MongoDBx::Class provides experimental, simple connection pooling for applications. Take a look at MongoDBx::Class::ConnectionPool for more information.

CAVEATS AND THINGS TO CONSIDER

There are a few caveats and important facts to take note of when using MongoDBx::Class as of today:

MongoDBx::Class's flexibility is dependant on its ability to recognize which class a document in a MongoDB collection expands to. Currently, MongoDBx::Class requires every document to have an attribute called "_class" that contains the name of the document class to use. This isn't very comfortable, but works. I'm still thinking of ways to expand documents without this. This pretty much means that you will have to perform some preparations to use existing MongoDB database with MongoDBx::Class - you will have to update every document in the database with the "_class" attribute.

The '_id' attribute of all your documents has to be an internally generated MongoDB::OID. This limitation may or may not be lifted in the future.

TUTORIAL

To start using MongoDBx::Class, please read MongoDBx::Class::Tutorial. It also contains a list of frequently asked questions.

ATTRIBUTES

namespace

A string representing the namespace of the MongoDB schema used (e.g. MyApp::Schema). Your document classes, structurally speaking, should be descendants of this namespace (e.g. MyApp::Schema::Article, MyApp::Schema::Post).

search_dirs

An array-ref of directories in which to search for the document classes. Not required, useful if for some reason MongoDBx::Class can't find your document classes.

doc_classes

A hash-ref of document classes found when loading the schema.

CLASS METHODS

new( namespace => $namespace )

Creates a new instance of this module. Requires the namespace of the database schema to use. The schema will be immediately loaded, but no connection to a MongoDB server is made yet.

OBJECT METHODS

connect( %options )

Initiates a new connection to a MongoDB server running on a certain host and listening to a certain port. %options is the hash of attributes that can be passed to new() in MongoDB::Connection, plus the 'safe' attribute from MongoDBx::Class::Connection. You're mostly expected to provide the 'host' and 'port' options. If a host is not provided, 'localhost' is used. If a port is not provided, 27017 (MongoDB's default port) is used. Returns a MongoDBx::Class::Connection object.

NOTE: Since version 0.7, the created connection object isn't saved in the top MongoDBx::Class object, but only returned, in order to be more like how connection is made in MongoDB (and to allow multiple connections). This change breaks backwords compatibility.